Plate tectonics vocab

Asthenosphere

solid, plastic layer of mantle beneath lithosphere; made of mantle rock flowing slowly, allows plates to move on top of it

continental drift hypothesis

developed by Alfred Wegener, suggested all present continents once existed assingle supercontinent, began breaking apart 200 million years ago & "drifted" to present positions

continental volcanic arc

mountains formed by igneous activity b/c of subducting oceanic lithosphere beneath a continent

convergent plate boundary

boundary between two colliding plates (mountain building,ocean trenches, and volcanic islands)

Curie point

temperature above which a material loses its magnetization.

deep-ocean trench

valley in ocean created when one lithospheric plate subducts under another

divergent plate boundary

boundary between tectonic plates where two plates move away from each other, new crust created between them

fossil magnetism

natural remnant magnetism in rock bodies. permanent magnetization acquired by rock used to determine location of magnetic poles & latitude of rock at time it became magnetized.

fracture zone

linear zone of irregular topography on deep-ocean floor that follows transform faults and their inactive extensions

hot spot

concentration of heat in mantle capable of producing magma,rises to Earth's surface ( ex: pacific Plate moves over a hot spot, producing the Hawaiian Islands)

lithosphere

solid, outer layer of earth that consists of crust and rigid upper part of mantle

magnetic reversal

switch in direction of Earth's magnetic field (magnetic north pole becomes magnetic south pole & magnetic south pole becomes the magnetic north pole)

mantle plume

buoyant mass of hot rock rising through Earth's mantle. As it nears Earth's surface, some of plume melts & erupts at surface forming "hot spot."

normal polarity

magnetic field the same as the present field.

oceanic ridge system

system of continuous elevated zones on floor of all major ocean basins. rifts at crests of ridges represent divergent plate boundaries.

paleomagnetism

study of the alignment of magnetic minerals in rock, relating to reversal of Earth's magnetic poles & magnetic properties rock requires during formation

Pangaea

single landmass that broke apart 200 million years ago and turned into today's continents

partial melting

process where most igneous rocks melt. individual minerals have different melting points, so most igneous rocks melt over a temperature range of a few hundred degrees. If liquid squeezed out after some melting occurred, melt with a higher silica content results.

plate

section of the lithosphere that slowly moves over the asthenosphere, carrying pieces of continental and oceanic crust

plate tectonics

theory that pieces of Earth's lithosphere are in constant motion, driven by convection currents in mantle

reverse polarity

magnetic field opposite to present field

ridge-push

force of gravity moves a plate downward and away from a ridge

rift (rift valley)

material displaced downward along spreading centers on continents often creates downfaulted valley.

seafloor spreading

process that creates new sea floor as plates move away from each other at the mid-ocean ridges

slab-pull

pulling of a tectonic plate as its edge subducts deep into mantle

subduction zone

region where an oceanic plate sinks down into asthenosphere at convergent boundary

transform boundary

plate boundary where two plates slide past each other in opposite directions

volcanic island arc

..., a chain of volcanic islands generally located a few hundred kilometers from a trench where there is active subduction of one oceanic plate beneath another